Method of descaling ferrous metals



solution of ferric chloride (F8013).

Patented Mar. 24, 1953 METHOD OF DESCALING FERROUS METAL Nathan H. Brodell, Canton, Ohio, assignor, by mesne assignments, to William Isler, Cleveland Heights, Ohio No Drawing. Application August 21, 1946, Serial No. 692,142

14 Claims. (Cl. 134-4) This invention relates, as indicated, to a method of descaling ferrous metals, but has reference more particularly to the descaling of ferrous metal articles, such as castings, forgings, bar stock, tubing, etc.

A primary object of the invention is to provide a method of the character described, which is I effective to remove scale from such articles in an inexpensive but highly efficient manner, and the use of which is free from objections which are inherent in conventional descaling methods, such as pickling, sand blasting, shot blasting, and the treatment methods, such as annealing and hardening.

A still further object of the invention is to provide a method of the character described, which is effective to remove scale from portions of ferrous metal articles which are usually inaccessible by sand and shot blasting methods, such as recesses and corners in intricate castings and forgings.

Other objects and advantages of the invention will be apparent during the course of the following description.

In accordance with the invention, the scalebearing articles, as for example, steel forgings, are first immersed in a saturated aqueous or other The solution of ferric chloride is preferably at room temperature, but may be at any temperature below the boiling point of the solution. The scale-bearing articles are also preferably at room temperature, but may also be at any temperature below the boiling point of the solution. In practice, however, the articles, prior to immersion, should be at a temperature not in excess of about 150 F. The articles, as stated, are immersed in the solution of ferric chloride which forms a glossy crystalline coating when dried. By using a saturated solution of ferric chloride, a maximum number of ferric chloride crystals are deposited ,unon bs-sur ace 9 h a t cles Weakeracueeus or other solutions of ferric chloride, may however, be employed with desirable results. If the articles, when immersed, are at a temperature above the boiling point of the solution, undesirable chemical changes occur in the solution.

After the coating has been thus formed on the articles, they are removed from the solution, and are permitted to dry. In some cases, however, the articles may be subjected to the next step in the treatment before the coating has dried. This next step consists in subjecting the coated articles to a conventional anneal in an annealing furnace, or to a conventional heat treatment which is a part of a hardening of the article. Such anneal or other heat treatment usually involves heating the articles to a temperature above 1200 F. and maintaining the articles at such temperature for a predetermined period of time. This anneal or other heat treatment causes the ferric chloride to break down to form'ferrous chloride, free iron, or iron oxide, ora combination of two or more of these, with a liberation or evolution of chlorine. The chlorine, thus liberated or evolved, has an oxidizing eifect on the scale, which tends to loosen the scale.

Following this treatment, the articles are removed from the heat treating furnace, and quenched in a solution of caustic soda (NaOI-I), which is preferably a 10% aqueous solution of caustic soda. The articles are preferably quenched before they have cooled to a temperature below about 1100 ,F., but good results have been obtained when the articles are quenched from a temperature as low as about 800 F. The solution of caustic soda, prior to such quenching treatment, may be at any temperature from room temperature to the boiling pointof the solution. This quenching treatment causes the loosened scale to fall away from the articles, and leaves them with a smooth, clean, mottled appearance.

In order to avoid injury to thehands of the operator when handling the articles after they have been removed from the quenching bath, any slight traces of caustic soda which adhere to the articles are preferably removed by rinsing them in hot or cold water.

The method, as thus described, removes scale from the articles in an inexpensive and highly efficient manner, and is particularly advantageous in that it removes scale from recesses and corners in intricate castings and forgings which are usually inaccessible by sand blasting methods. Moreover, the chemicals which are employed are available in commercially desirable quantities at relatively low cost. A further advantage lies in the fact that the heat treatment which is a part of the method serves the double purpose of annealing or hardening the article and breaking down the coating to loosen the scale on the article.

The ferric chloride may, if desired, be added directly to the furnace either in crystalline form, or as a vapor, gas, or liquid, the ferric chloride in this form reacting with the scale to loosen the scale.

Instead of using ferric chloride as the oxidizing agent, other chlorides of polyvalent metals may be used with satisfactory results, such, for example, as stannic chloride, cupric chloride and mercuric chloride, As a matter of fact, any completely oxidized polyvalent metallic halide is effective to produce satisfactory results. Organic compounds having physical properties similar to such metallic halides may also be used, such organic compounds being those included under the generic name of aliphatic and aromatic polyhalides. Carbon tetrachloride has also been used, with good results.

Instead of using caustic soda as the solution in which the articles are quenched, other compo h a odium carb nat (Naoon, may be used with fairly good results. other quench s media, u as a 1 aque us solution of sodium chloride, o at alone, maybe used, as thes furnish a suffic ntly drastic quench- In some ca pa t cula ly whe e it is desired to ard t a ic e oi may be us d as a u nching medium.

n tea o imm rs ng the articles in the qu n m dia, the quenching medium can be sprayed onto the articles,

It will be un rsto d that the various chan s in temperatures, strengths of solutions, and other details of the method may be resorted to, Withut d parting from the scope f the subioined claims.

Having thus described my invention, I claim:

1. In a method of descalin errous metal articles, the steps which consist in immersing the articles in a solution of a compound sel cted from th r up consistin of compl t ly oxidiz d polyvalent metallic halides and aliphatic and aromatic po y lides to f rm a coating of said compound on said article. then heating the articles to a temperature such that a chemical change in the coating loosens the scale on said articles, and then quenching the articles in a solution of a compound which b eaks the scale away from the articles.

2. n a me ho of de aling f rrous metal arl t e st ps which consist in subjecting the articles to the action or a halide selected from t r up onsistin f compl y oxidized polyvalent metallic halides and aliphatic and aromatic polyhalides, whereb a coating is formed on the articles, heating the articles to a tem- Derature such th t a h mi l chan e in th coatin l os ns the scal on said articles, n then quenching the articles in. a medium which causes the scale tobe broken. away from. sai articles.

3. A method, as defined in claim 2, in which the halide is selected from the group of completely oxidized polyvalent metallic halides.

4. A method, as defined in claim 2, in which the quenching medium is water.

5. A method, as defined in claim 2, in which the quenching medium is sprayed onto the articles.

6. In a method of descaling ferrous metal articles, the steps which consist in subjecting the articles to a solution of a chloride selected from the group consisting of completely oxidized polyvalent metallic chlorides and carbon tetrachloride, whereby a coating is formed on the articles, heating the articles to a temperature such that a chemical change in the coating loosens the scale on said articles, and then quenching the articles in a solution of a sodium compound to cause the scale to be broken away from said articles.

7. In a method of descaling ferrous metal articles, the steps which consist in immersing the articles in a solution of a chloride selected from the group consisting of completely oxidized polyvalent metallic chlorides and carbon tetrachloride, whereby a coating is formed on the articles, heating the articles to a temperature such that a chemical change in the coating loosens the scale on said articles, and then quenching the articles in a solution of a sodium compound, whereby to cause the scale to be broken away from said articles.

8. In a method of descaling ferrous metal articles, the steps which consist in immersing the articles in a solution of a chloride selected from the group consisting of completely oxidized polyvalent metallic chlorides and carbon tetrachloride, whereby a coating of the chloride is formed on the articles, heating the articles to a temperature which causes a breakdown of the chloride and a loosening of the scale on the articles, and then quenching the articles in a solution of a sodium compound, whereby to cause the scale to be broken away from said articles.

9. A method, as defined in claim 8, in which said sodium compound is one selected from the group consisting of sodium hydroxide and sodium carbonate.

10. In a method of descaling ferrous metal articles, the steps which consist in immersing the articles in an aqueous solution of ferric chloride to form a coating of said chloride on the articles, heating the articles to a temperature in excess of about 800 F., to loosen the scale, and then quenching the articles in a solution of sodium hydroxide.

11. In a method of descaling ferrous metal articles, the steps which consist in immersing the articles in a saturated solution of ferric chloride to form a coating of said chloride on the articles, heating the articles to a temperature in excess of about 800 F., to cause a breakdown of the chloride to ferrous chloride, thereby loosening the scale on the articles, and then quenching the articles in a solution of sodium hydroxide, whereby the scale falls away from the articles.

12. A method, as defined in claim 11, in which the last-named solution is a 10% aqueous solution of sodium hydroxide.

13. In a method of descaling ferrous metal articles, the steps which consist in coating the articles with a solution of ferric chloride, heating the articles to a temperature in excess of about 800 F., to loosen the scale, and then removing the loosened scale from the articles.

14. In a method of descaling ferrous metal articles, the steps which consist in coating the articles with ferric chloride, heating the articles to a temperature in excess of about 800 F., to

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 33,844 McDaniel Dec. 3, 1861 1,373,573 Sorenson Apr. 5, 1921 1,898,809 Berg Feb. 21, 1933 Number 6 Name Date McDorman June 9, 1936 Bassett July 28, 1942 Caugherty Jan. 4, 1944 Keene May 2, 1944 Dyer July 4, 1944 Young July 10, 1945 Felber June 1, 1948 OTHER REFERENCES Mellor: Modern Inorganic Chemistry, page 819, Longmans Green and Company, New York, 1939. (Copy in Division 27.) 

1. IN A METHOD OF DESCALING FERROUS METAL ARTICLES, THE STEPS WHICH CONSIST IN IMMERSING THE ARTICLES IN A SOLUTION OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF COMPLETELY OXIDIZED POLYVALENT METALLIC HALDES AND ALIPHATIC AND AROMATIC POLYHALIDES TO FORM A COATING OF SAID COMPOUND ON SAID ARTICLE, THEN HEATING THE ARTICLES TO A TEMPERATURE SUCH THAT A CHEMICAL CHANGE IN THE COATING LOOSENS THE SCALE ON SAID ARTICLES, AND THEN QUENCHING THE ARTICLES IN A SOLUTION OF A COMPOUND WHICH BREAKS THE SCALE AWAY FROM THE ARTICLES. 